The attack in Brussels may have been shocking, but it was hardly surprising that Europe was subject to a coordinated terrorist campaign directed by the Islamic State (ISIS). As European officials reported in the days after the strike, ISIS had previously dispatched “at least 400 fighters to target Europe.” These terrorists, mostly of European origin, were instructed to construct “interlocking terror cells,” officials say, and were given autonomy to choose their target, timing, and methods. It is likely that the March bloodshed is not the last that Europe will see from these networks.

By now the pattern is well established. Fighters, after spending some time with ISIS proper in Syria or Iraq, return home to link up with brothers and childhood friends, who may have also made a pilgrimage to the Islamic State, and pals with whom they have forged bonds while learning to kill in Syria. They try to take the tactics of insurgency to the streets of Europe, killing civilians and targeting government installations. If they fail, they move on to the next plot. And if they succeed, they also move on to the next plot.

NETWORKED DANGER

Abdelhamid Abaaoud was the operations manager of the coordinated attacks on cafes, a stadium, and a concert hall in Paris on November 13, 2015. He should have been in prison at that point. In July 2015, he had been convicted and sentenced to 20 years in connection with another foiled plot in the Belgian city of Verviers. Some time between the foiled Verviers plots, in which two suspects died, and the Paris attack, Abaaoud managed to travel back to the Islamic State and then return to Europe later in 2015. From that point, the French government says, he coordinated four out of six foiled attacks targeting France since the spring.

Abaaoud was not the only man to walk away from last fall’s carnage in Paris. His old friend from Molenbeek, Salah Abdeslam, walked away, too, and returned to Brussels. Later analysis of Abaaoud’s telephone showed